Optical sensor

Abstract

Optical sensor (1) with at least one transmitter (4) emitting light beams (3), with at least one receiver (6) which is designed to receive the light beams (3) of the transmitter (4), with at least one amplifier stage in which a received signal from the receiver (6) is amplified, and with at least one threshold switch (12, 12a, 12b, 12c) in which the amplified received signal is digitized, and with an evaluation unit (9) in which an output signal is generated depending on the digitized received signal, characterized in that at least one switching unit (14) is provided, by means of which the received signal is switched to one of a plurality of receive paths with an amplifier stage and / or a threshold switch (12, 12a, 12b, 12c), so that the received signal is fed to the evaluation unit (9) only via the switched receive path.

Description

The invention relates to an optical sensor.The optical sensor serves in particular for detecting objects in a monitoring region. For this purpose, the optical sensor comprises at least one light beam emitting transmitter and a light beam receiving receiver. Furthermore, the optical sensor comprises an evaluation unit in which an object detection signal is generated as a function of received signals of the receiver.Typically, the optical sensor operates according to the light barrier principle, so that object detection is carried out by registering an interruption of the beam path of the light beams that pass through the monitoring area.In the case where the optical sensor has only one transmitter or receiver, it is designed as a light barrier or reflection light barrier. If the optical sensor has a plurality of pairs of transmitters and receivers, it is designed as a light curtain or reflex light curtain.Reception signals of the receiver are generally amplified in an amplifier stage before they are fed to the evaluation unit.The amplifier stage, which in the simplest case can be formed by a single amplifier, is advantageously set, before the optical sensor is put into operation, to a working point at which the amplifier stage is operated in a working mode.Since objects to be detected can be arranged at different distances from the optical sensor and / or, due to greatly varying surface properties of the objects, greatly varying amplitudes of the received signals can be obtained in object detections, i.e. the amplifier stage requires a high dynamic range.However, this dynamic range cannot be realized or can be realized only incompletely in known amplifier stages, so that when the received signals are amplified in the amplifier stage, signal distortions of the received signals and overdrives of the amplifier stage occur, which can lead to considerable adverse effects during object detection.The object of the invention is to provide an optical sensor of the type mentioned at the beginning, in which reliable and reliable object detection is ensured.To achieve this object, the features of claim 1 are provided. Advantageous embodiments of the invention are described in the dependent claims.The invention relates to an optical sensor having at least one light beam emitting transmitter and at least one receiver which is designed to receive the light beams from the transmitter. Furthermore, at least one amplifier stage is provided in which a received signal of the receiver is amplified. The amplified received signal is digitized by at least one threshold switch. Furthermore, the optical sensor has an evaluation unit in which an output signal is generated as a function of the digitized received signal. At least one switching unit is provided by means of which the received signal is connected to one of a plurality of reception paths with an amplifier stage and / or a threshold switch. The received signal is supplied to the evaluation unit only via the connected receive path.The basic idea of the invention is to use the switching unit assigned to the at least one receiver to perform a switching between different reception paths. In each of the individual reception paths, at least one amplifier stage and / or at least one threshold switch is present. The amplifier stages of the reception paths differ in terms of their amplification properties, the threshold switches of the reception paths differ in terms of their modes of operation in the digitalization of amplified reception signals.The switchover is effected with the switchover unit in such a way that the optimum reception path for the further processing of the received signals is selected. In this case, in particular the reception path is selected whose amplifier stage ensures distortion-free amplification of the reception signals. The amplifier stage of the selected reception path operates in a range in which no overdrives occur. Alternatively or additionally, the threshold switch which is most suitable for the received signals is also selected.This achieves the essential advantage that, during the processing of the received signals in the amplifier stage or in the threshold switch, no signal corruptions occur in the reception path selected by the switching unit, which could lead to erroneous detections of the optical sensor.The construction of the optical sensor according to the invention is advantageously such that the at least one receiver is formed by a photodiode.Of course, other receiver designs are also possible, such as phototransistors, avalanche diodes and the like.Accordingly, the transmitter of the optical sensor can be formed by a light emitting diode or a laser diode.The or each changeover unit of the optical sensor according to the invention advantageously consists of an arrangement of signal changeover switches.The number of signal switches is matched to the number and structures of the individual reception paths.A signal changeover switch is advantageously formed by an analog switch, a MOSFET transistor or a multiplier.According to a further advantageous embodiment, a signal changeover switch is formed by an arrangement of diodes.Low-capacitance diodes, such as PIN diodes, are particularly suitable for forming signal changeover switches.According to a specific embodiment, at least one signal changeover switch is present, by means of which a changeover can be carried out between a plurality of parallel reception paths, each having an amplifier stage.Furthermore, at least one signal changeover switch can be present, by means of which a changeover can be carried out between a plurality of parallel reception paths each having a threshold value switch.According to an advantageous development, a series arrangement of signal changeover switches is present, it being possible to perform a changeover between a plurality of parallel partial reception paths, each having an amplifier stage and / or a threshold value switch, by means of each signal changeover switch in a reception path.This embodiment is furthermore advantageous if the received signals are amplified multiple times in a multistage arrangement of amplifier stages. A plurality of partial reception paths with different amplifier stages can then be provided for the individual stages, which paths can be switched over in each case by means of a signal changeover switch. Partial reception paths with different threshold switches can also be incorporated in such structures.An important advantage of the invention is that a selection of a reception path optimized to the properties as reception signals is selected with the switching units for processing the reception signals, namely in such a way that signal corruptions of the reception signals are avoided or largely excluded.This makes it possible for the amplifier stages and / or threshold switches in the reception paths to be operated unchanged in a predefined operating state.This simplifies the reception signal processing considerably, since there is no need to track amplifier stages or threshold switches to current reception signals.According to an advantageous embodiment, the operating states of the amplifier stages and / or threshold switches are fixed at the factory.In this case, the amplifier stage can be fixed to an optimized operating point. The operating state is then maintained in the working operation of the optical sensor.In particular, the operating state of an amplifier stage is determined by a predefined distortion behavior and / or a predefined overload behavior.Furthermore, the operating state of a threshold value switch is determined by evaluations of rising and / or falling edges of received signals and / or temporal hysteresis and / or amplitude hysteresis.According to an advantageous embodiment, the or each switching unit is controlled by a controller, wherein the controller expediently controls signal switches of the switching unit.With the control, selection of reception paths effected by the switching unit through the switching of the reception paths can be flexibly adapted to varying reception signals, so that the subsequent amplification of the reception signal in the or each amplifier stage can take place without distortion in the selected reception path.In the case where a plurality of switching units are present, the controller may control each switching unit individually. Alternatively, groups of switching units or all switching units can be controlled jointly, i.e. in the same way and simultaneously, by the controller.The type of control can be predefined depending on the configuration of the optical sensor or depending on the respective application.According to a first variant, the suitable reception paths are determined by the controller in a learning process and are retained unchanged in a subsequent working operation.According to a second variant, the suitable reception paths are permanently suitably switched over by the controller in a working mode.This variant is advantageous when the received signals change greatly during working operation. In operating operation, a fast and reliable adaptation to the received signals can then be achieved by controlling the changeover unit by a time-dependent selection of reception paths.In both variants, the reception pads are advantageously determined from magnitudes of the reception signals after amplification has been carried out in an amplifier stage and / or after digitization in a threshold switch.The magnitudes of the received signals can be, for example, when the transmitter emits light beams in the form of light pulses, pulse widths, pulse amplitudes and the like as characteristic variables of received signal pulses registered on the receiving side.The control values are thus continuously adapted to the current amplified received signals, wherein these current received signals show whether there is a risk or a trend toward overdrives or distortions in the received signals.According to an advantageous development, control processes are carried out with the controller.The optical sensor according to the invention can be designed in different embodiments.According to a first embodiment, this is a data transmission unit.In particular, the optical sensor can be designed as a data light barrier. Codes containing information are impressed on the light beams of the transmitter, which codes are received in the receiver and decoded in the evaluation unit.Furthermore, the optical sensor can be a code reader, in particular a barcode reader. The light beams emitted by the transmitter are periodically deflected by means of a deflection unit and are guided over codes to be detected. On the basis of the received signals obtained by the receiver, the codes are decoded in the evaluation unit.Furthermore, the optical sensor can be a measuring device for ascertaining optical measurement variables.The measured variables can be, for example, geometry variables of objects.According to an advantageous embodiment, the optical sensor is designed to detect objects in a monitoring area.In this case, it generates an object detection signal as an output signal.The object detection signal can be, in particular, a binary switching signal, the switching states of which indicate whether or not an object is located in the monitored zone.According to an advantageous embodiment, the transmitter and the receiver of the optical sensor form a light barrier arrangement. The object detection takes place according to the light barrier principle.If the optical sensor has a plurality of transmitter-receiver pairs, the optical sensor forms a light curtain.In this configuration, the transmitter and receiver of the or each transmitter-receiver pair are located at opposite edges of a surveillance area. In the case of a free monitoring region, the light beams of the transmitter forming the measurement paths strike the associated receiver in each transmitter-receiver pair, which is registered in the evaluation unit on the basis of the analysis. In the event of object intervention in the monitoring region, the beam path of the light beams of the or at least one transmitter-receiver pair is interrupted.According to a further advantageous embodiment, the transmitter and the receiver of the optical sensor form a reflection light barrier arrangement. If this optical sensor has a plurality of transmitter-receiver pairs, this forms a reflex light curtain.The transmitter and receiver of the or each transmitter-receiver pair are then arranged at an edge of the monitored zone. A reflector is located at the other edge of the monitoring region. With the monitoring area free, the light beams of the transmitter of a transmitter-receiver pair pass unimpeded to the reflector and are guided at the latter back to the associated receiver. In the event of object intervention, the beam path of the light beams of at least one transmitter is interrupted.When the optical sensor is designed as a light curtain, according to a first embodiment, each receiver is assigned a changeover unit.According to a preferred embodiment, one or more multiplexers are present. By means of these, in a multiplex mode, the received signals of all receivers or of a group of receivers of a switching unit are connected in.The switching unit and the multiplexer or multiplexers can generally form separate units.Alternatively, the or each multiplexer forms the switching unit. In this case, the multiplexer or multiplexers are constructed from switching diodes.According to an advantageous embodiment, the optical sensor is designed as a safety sensor. Such a safety sensor can be used in safety applications, in particular in the field of personal protection. For this purpose, the safety sensor has a failsafe structure.This can be realized in that the optical sensor has a two-channel evaluation unit, in particular in the form of two computer units which monitor each other cyclically.The error-proofness of the optical sensor is further increased by the fact that it has test means for testing the switchover unit and / or elements of the reception paths.The test means are advantageously a component of the evaluation unit.According to an advantageous embodiment, a switching of a reception path takes place via a channel of the evaluation unit. Changes in amplification properties caused by this are checked for the received signals via the further or both channels of the evaluation unit.Furthermore, it is possible that these predetermined time intervals are changed for testing the switching over of a reception path. Switching units are tested by ascertaining the signal differences of received signals with and without activation.The invention is explained below with reference to the drawings. The following are shown: FIG. 1 : Exemplary embodiment of the optical sensor according to the invention in the form of a light barrier. FIG. 2 : Exemplary embodiment of the optical sensor according to the invention in the form of a light curtain. FIG. 3 : Receiving-side circuit arrangement for an optical sensor according to the prior art. FIGS. 4a-d show signal curves of signals of the optical sensor without distortions during overload. FIGS. 5a-d show signal curves of signals of the optical sensor with distortions during overload. FIGS. 6a-d show signal curves of signals of the optical sensor with distortions and overshoots. FIG. 7 : First block diagram of a receiving-side circuit arrangement according to the invention. FIG. 8 : Second block diagram of a receiving-side circuit arrangement according to the invention. FIG. 9 : Third block diagram of a circuit arrangement according to the invention on the receiving side. FIG. 10 : Fourth block diagram of a receiving-side circuit arrangement according to the invention. FIG. 11 : Fifth block diagram of a receiving-side circuit arrangement according to the invention.FIG. 1 shows an exemplary embodiment of the optical sensor 1 according to the invention in the form of a light barrier.The light barrier has a first housing 2 a, in which a transmitter 4 emitting light beams 3 is arranged, to which a transmission optics 5 is assigned. Furthermore, the light barrier has a second housing 2 b, in which a receiver 6 receiving light beams 3 with a receiving optics 7 arranged upstream is arranged. The transmitter 4 can be formed by a light-emitting diode, and the receiver 6 by a photodiode.The housings 2 a, 2 bare arranged on opposite edges of a monitoring region in such a way that, in the case of a free monitoring region, the light beams 3 impinge on the receiver 6 in an unimpeded manner, running analogously to a measurement path. In the event of an object intervention in the monitoring region, the light beams 3 are interrupted.The transmitter 4 is controlled by a transmitter controller 8. An evaluation unit 9 is assigned to the receiver 6. The evaluation unit 9 controls the receiver 6 and evaluates the received signals of the receivers 6, as a result of which a binary switching signal is generated as the object detection signal, the switching states of which signal indicate whether an object is located in the monitored zone or not.The evaluation unit 9 can have a multi-channel construction if the light barrier is a safety sensor.FIG. 2 schematically shows the structure of an exemplary embodiment of the optical sensor 1 according to the invention in the form of a light curtain for detecting objects within a monitoring region.The light curtain has a first housing 2 awith a series arrangement of transmitters 4 emitting light beams 3 and transmission optics 5 assigned to these. Furthermore, the light curtain has a second housing 2 bhaving a row arrangement of receivers 6 receiving light beams 3, which are each preceded by a receiving optical unit 7.The housings 2 a, 2 bare arranged on opposite edges of the monitoring region in such a way that a receiver 6 is arranged opposite a transmitter 4 in each case. This transmitter-receiver pair forms a beam axis. In the present case, six beam axes are provided. Of course, the light curtain can also have a different number of beam axes.The transmitters 4 are controlled by a transmitter controller 8. An evaluation unit 9 is assigned to the receivers 6. In this case, the beam axes are activated cyclically one after the other. The evaluation unit 9 controls the receivers 6 and evaluates the received signals of the receivers 6 to generate a binary switching signal, the switching states of which indicate whether an object is located in the monitored zone or not. In general, this evaluation can be carried out not only in a time sequence successively for a plurality of light beams 3 but also simultaneously for a plurality of light beams 3. In the case of a free monitored region, the light beams 3 of the beam axes pass unimpeded to the receiver 6 of the respective beam axis. In the event of an object intervention, at least one beam axis is interrupted. The evaluation unit 9 can have a multi-channel construction if the light curtain forms a safety sensor.FIG. 3 shows a receiving-side circuit arrangement for a light barrier, i.e. an optical sensor 1 according to FIG. 1, as is known from the prior art.FIG. 3 shows a receiver 6 in the form of a photodiode which receives light beams 3 from the transmitter 4. A resistor 10 generates a bias voltage for the receiver 6.Received signals generated in the receiver 6 are fed to an amplifier stage which in the present case is formed only by an amplifier 11, which is not obligatory, however.The received signals amplified in the amplifier 11 are fed to a threshold value switch 12 and digitized there. In this case, the operating state of a threshold value switch 12 is determined by evaluations of rising and / or falling edges of received signals and / or temporal hysteresis and / or amplitude hysteresis. The digitized received signals are fed to an evaluation logic 13 which is a component of the evaluation unit 9. There, the object detection signal is generated depending on the received signals.FIGS. 4a to 4d show time diagrams of signal curves for the optical sensor 1 according to FIG. 1 with the circuit arrangement according to FIG. 3.In the present case, the transmitter 4 emits light beams 3 in the form of sequences of light pulses, wherein two light pulses are shown in FIG. 4 a.FIG. 4 bshows time curves of the analog received signal of the receiver 6 when receiving the light pulse according to FIG. 4 a. A reception signal with a small amplitude is shown in dash-dot lines. Furthermore, a reception signal with a large amplitude is shown with a solid line.FIG. 4 cshows the digitized received signal obtained at the output of the threshold switch 12 for the non-overdriven received signal with small amplitude according to FIG. 4 b. In accordance with the received light pulses, received signal pulses with pulse widths Tp are obtained, wherein the rising edges of the received signal pulses are offset by the time T 1 and the falling edges are offset by the time T 2.FIG. 4 d shows the received signal obtained at the output of the threshold switch 12 for the received signal with a large amplitude according to FIG. 4 b. Due to the different amplitudes of the received signal, digitized received signal pulses P 1, P 2 are obtained, whose pulse widths Tpand their time intervals T 1', T 2 are distorted, which can lead to erroneous detections.FIGS. 5a to 5d show further time diagrams of signal curves for the optical sensor 1 according to FIG. 1 with the circuit arrangement according to FIG. 3.FIG. 5a shows, analogously to FIG. 4a, the time profile of light pulses which are emitted by the transmitter 4.FIG. 5 bshows the temporal profile of the analog received signals of the receiver 6 without distortion for the light pulses according to FIG. 5 a.In this case, the error-free received signal pulses are obtained at the output of the threshold switch 12, as shown in FIG. 4 c.FIG. 5 cshows the time profile of the analog received signals of the receiver 6 with distortion for the light pulses according to FIG. 5 a.As a result of the distortions, digitized received signal pulses P 1, P 2 having distorted pulse widths T 11, T 21 and distorted time intervals T 1', T 2' are obtained at the output of the threshold switch 12, which can lead to erroneous detections.FIGS. 6a to 6d show further time diagrams of signal curves for the optical sensor 1 according to FIG. 1 with the circuit arrangement according to FIG. 3.FIG. 6a shows, analogously to FIG. 4a, the time profile of light pulses which are emitted by the transmitter 4.FIG. 6 bshows the temporal profile of the analog received signals of the receiver 6 without distortion for the light pulses according to FIG. 6 a.In this case, the error-free received signal pulses are obtained at the output of the threshold switch 12, as shown in FIG. 4 c.FIG. 6 cshows the time profile of the analog received signals of the receiver 6 with overshoots for the light pulses according to FIG. 5 a.As a result of the distortions, digitized received signal pulses P 1, P 2 having distorted pulse widths T 11, T 21 and distorted time intervals T 1', T 2' are obtained at the output of the threshold switch 12, which can lead to erroneous detections.The overshoots U 1, U 2 generate additional digitized received signal pulses P 1, P 2 at the output of the threshold value switch 12, which may lead to erroneous detections.Corresponding signal curves are also obtained for the receivers 6 of the light curtain according to FIG. 2.FIG. 7 shows an exemplary embodiment of the inventive receiving-side circuit arrangement for the light barrier according to FIG. 1.The circuit arrangement corresponds to the arrangement according to FIG. 3 in that a receiver 6 in the form of a photodiode, a threshold value switch 12 and an evaluation logic 13 are provided as a component of the evaluation unit 9.According to the invention, a switching unit 14 is provided, which in the present case has two signal switches 15 a, 15 b. Such a signal changeover switch 15 a, 15 bis advantageously formed by an analog switch, a MOSFET transistor or a multiplier.Alternatively, a signal changeover switch 15 a, 15 bis formed by an arrangement of diodes.The evaluation logic 13 forms a control for the changeover unit 14. For this purpose, a control line 16 leads from the evaluation logic 13 to the signal changeover switches 15 a, 15 b.A changeover between three reception paths can be carried out with the changeover unit 14, wherein a first amplifier stage in the form of a first amplifier 11 ais present in a first reception path, a second amplifier stage in the form of a second amplifier 11 bis present in a second reception path, and a third amplifier stage in the form of a third amplifier 11 cis present in a third reception path.Advantageously, the amplifier stages have non-linear and / or frequency-dependent amplification properties.In this case, the operating state of an amplifier stage is determined by a predefined distortion behavior and / or a predefined overload behavior.The design of amplifier stages in the form of individual amplifiers 11 ato 11 cis not obligatory.Instead of amplifier stages, attenuators, such as voltage dividers, can also be used which have a gain of less than 1.The reception signal is only connected to one reception path by the switching unit 14, so that the reception signal is amplified only in the amplifier 11 a, 11 bor 11 cof this reception path.With the control, depending on currently registered, amplified received signals, that receive path is selected whose amplifier 11 ato 11 cis best matched to the received signals. The individual amplifiers 11 ato 11 care set to different operating points before the optical sensor 1 is put into operation. The switching unit 14 then selects the amplifier stage in which the received signals are amplified without distortion and without overdrives, i.e. errors as shown in FIGS. 4 to 6 are avoided.The amplifiers 11 ato 11 cdo not have to be tracked in the operating mode of the optical sensor 1, i.e. they can be operated constantly in a predefined operating state, wherein the operating states can be fixed at the factory. The operating state of an amplifier stage is advantageously determined by a predefined distortion behavior and / or a predefined overload behavior.If the optical sensor 1 is designed in the form of a light curtain according to FIG. 2, the circuit arrangement according to FIG. 7 can be provided for each of the receivers 6 of the light curtain.In addition, a multiplexer can be provided, with which the received signals of different receivers 6 of the light curtain are fed individually one after the other to the circuit arrangement according to FIG. 7. Such arrangements are shown in Figs. 10 and 11.The following exemplary embodiments of FIGS. 8 and 9, which, like FIG. 7, show a circuit arrangement for a light barrier, can be extended to a light curtain in the same way.The embodiment of FIG. 8 is extended compared to the embodiment of FIG. 9 in that two series-connected amplifier arrangements are provided.Analogously to the embodiment according to FIG. 7, the received signals are selectively connected to an amplifier 11 a, 11 bor 11 cvia a changeover unit 14 consisting of signal changeover switches 15 a, 15 b, which are arranged in separate partial reception paths.A further changeover unit 14 consisting of signal changeover switches 15 c, 15 dis then connected. With this changeover unit 14, the received signals amplified in the first amplifier arrangement are amplified again, to be precise depending on the switching state of the signal changeover switch 15 cin one of the amplifiers 11 d, 11 e, 11 fwhich are arranged in different partial reception paths and form the second amplifier arrangement.By means of the signal changeover switch 15d, the doubly amplified received signal is then selectively connected to one of two threshold value switches 12a, 12b, in which the received signal is digitized before it is fed to the evaluation logic 13.The threshold switches 12a, 12b differ in their operating states.In this case, the operating state of a threshold value switch 12 a, 12 bis determined by evaluations of rising and / or falling edges of received signals and / or temporal hysteresis and / or amplitude hysteresis if the transmitter or transmitters 4 emit light beams 3 in the form of light pulses.The evaluation logic 13 forms a control for all the changeover units 14. For this purpose, control lines 16 lead from the evaluation logic 13 to the individual signal changeover switches 15 ato 15 d.Depending on the currently registered received signals, the control of the signal switches 15 ato 15 dis performed so that an application to one of the amplifiers 11 ato 11 cand an application to the amplifiers 11 dto 11 fare carried out, wherein the amplifiers 11 ato 11 cor 11 dto 11 f, which are optimal for distortion-free amplification, are selected in each case. Likewise, by controlling the signal changeover switch 15 d, the threshold value switch 12 a, 12 bfor digitizing the received signals is selected in an optimized manner for the current received signals.FIG. 9 shows a variant of the embodiment according to FIG. 8.Analogously to the embodiment according to FIG. 8, the reception signal of the receiver 6 is also amplified twice in a serial amplifier arrangement in the embodiment according to FIG. 9.The first amplifier arrangement again comprises amplifiers 11 ato 11 cin different sub-reception paths. With the changeover unit 14 consisting of the signal changeover switches 15 a, 15 b, the reception signal is connected to one of the amplifiers 11 ato 11 cin the individual partial reception paths by means of the control formed by the evaluation logic 13.The signal switcher 15 cof the second switcher 14 is used to connect the received signal amplified in the first amplifier arrangement to one of three partial reception paths. In this case, an amplifier 11 dis provided in a first partial reception path with threshold value switches 12 aarranged downstream. In a second partial reception path, an amplifier 11 eis present with threshold value switches 12 barranged downstream. In a third partial reception path, an amplifier 11f with a threshold value switch 12c arranged downstream is present. The outputs of these partial reception paths are fed to the evaluation logic 13.The mode of operation of the control formed by the evaluation logic 13 is such for the aforementioned embodiments that it controls the signal switches 15 ato 15 dwith defined control values.In this case, control values for controlling the reception paths can be determined in a learning process and retained unchanged in a subsequent working operation.Alternatively, control values for controlling the reception paths are continuously tracked in a working mode.In general, the control values are determined from magnitudes of the received signals after amplification has taken place in an amplifier stage and / or after digitalization in a threshold value switch 12 ato 12 c.According to an advantageous embodiment, the optical sensor 1 has test means for testing the switchover unit 14 and / or elements of the reception paths.The test means are advantageously a component of the evaluation unit 9.In particular, these predetermined time intervals are changed for testing the switching over of a reception path. The checking of switching units 14 is carried out by determining the signal differences of received signals with and without activation.If the optical sensor 1 is a safety sensor and if the evaluation unit 9 is embodied as multi-channel, a switching over of a reception path takes place via a channel of the evaluation unit 9. The changes in amplification properties for the received signals caused thereby are checked via the further or both channels of the evaluation unit 9.FIG. 10 shows a variant of the exemplary embodiment according to FIG. 7 of the inventive receiving-side circuit arrangement for a plurality of multiplexed receivers. With the switches 17 different receivers can be switched to the changeover switch 15a.FIG. 11 shows a particular variant of the embodiment according to FIG. 7, in which the signal switches 15a, 15a' bring about the switching to different receivers at the same time as the switching to different amplifiers 11a, 11b, 11c and the receivers are thus multiplexed.List of reference characters1 Optical sensor 2a Housing 2b Housing 3 Light beam 4 Transmitter 5 Transmission optics 6 Receiver 7 Reception optics 8 Transmitter controller 9 Evaluation unit 10 Resistor 11, a, b, c, d, e, f Amplifier 12, a, b, c Threshold value switch 13 Evaluation logic 14 Switching unit 15a, a', b, c, d Signal switch 16 Control line 17 Switch P1 Digitized received signal pulse P2 Digitized received signal pulse Tp Pulse width T11 Distorted pulse width T21 Distorted pulse width T1 Time T2 Time T1' Time interval T2' Time interval Ü1 Overshoot 2 Overshoot

Claims

Optical sensor (1) having at least one transmitter (4) emitting light beams (3), having at least one receiver (6) which is designed to receive the light beams (3) of the transmitter (4), having at least one amplifier stage in which a received signal of the receiver (6) is amplified, and having at least one threshold switch (12, 12a, 12b, 12c) in which the amplified received signal is digitized, and having an evaluation unit (9) in which an output signal is generated as a function of the digitized received signal, characterized in that at least one switching unit (14) is present, by means of which the received signal is connected to one of a plurality of reception paths having an amplifier stage and / or a threshold switch (12, 12a, 12b, 12c), with the result that the received signal is fed to the evaluation unit (9) only via the connected reception path.Optical sensor (1) according to Claim 1, characterized in that it is a data transmission unit.Optical sensor (1) according to claim 1, characterized in that it is a code reader.Optical sensor (1) according to Claim 1, characterized in that it is a measuring device for ascertaining optical measurement variables.Optical sensor (1) according to Claim 1, characterized in that it is designed for detecting objects in a monitored region.Optical sensor (1) according to Claim 5, characterized in that it generates an object detection signal as an output signal.Optical sensor (1) according to either of Claims 5 and 6, characterized in that it is a light barrier.Optical sensor (1) according to either of Claims 5 and 6, characterized in that it is a light curtain.Optical sensor (1) according to claim 8, characterised in that it comprises a multiple arrangement of transmitter-receiver pairs.Optical sensor (1) according to either of Claims 8 and 9, characterized in that each receiver (6) is assigned a changeover unit (14).Optical sensor (1) according to either of Claims 8 and 9, characterized in that one or more multiplexers are present, by means of which the reception signals of all receivers (6) or of a group of receivers (6) are connected to a switching unit (14) in multiplexed operation.Optical sensor according to Claim 11, characterized in that the or each multiplexer forms the switching unit (14).Optical sensor (1) according to one of Claims 1 to 12, characterized in that the switching unit (14) has an arrangement of signal changeover switches 15a to 15d.Optical sensor according to Claim 13, characterized in that a signal changeover switch 15a to 15d is formed by an analog switch, a MOSFET transistor or a multiplier.Optical sensor according to Claim 13, characterized in that a signal changeover switch (15a to 15d) is formed by an arrangement of diodes.Optical sensor according to one of Claims 13 to 15, characterized in that at least one signal changeover switch (15a to 15d) is present, by means of which a changeover can be carried out between a plurality of parallel reception paths each having an amplifier stage.Optical sensor according to one of Claims 13 to 16, characterized in that at least one signal changeover switch (15a to 15d) is present, by means of which a changeover can be carried out between a plurality of parallel reception paths which each have a threshold value switch (12, 12a, 12b, 12c).Optical sensor (1) according to one of Claims 16 or 17, characterized in that a series arrangement of signal changeover switches (15a to 15d) is present, it being possible by means of each signal changeover switch (15a to 15d) to carry out a changeover between a plurality of parallel partial reception paths each having an amplifier stage and / or a threshold value switch (12, 12a, 12b, 12c).Optical sensor (1) according to one of Claims 1 to 18, characterized in that the amplifier stages and / or the threshold switches (12, 12a, 12b, 12c) in the reception paths are operated unchanged in a predefined operating state.Optical sensor (1) according to Claim 19, characterized in that the operating states of the amplifier stages and / or of the threshold switches (12, 12a, 12b, 12c) are fixed at the factory.Optical sensor (1) according to one of Claims 19 or 20, characterized in that the operating state of an amplifier stage is determined by a predefined distortion behavior and / or a predefined overload behavior.Optical sensor (1) according to one of Claims 19 to 21, characterized in that the amplifier stages have nonlinear and / or frequency-dependent amplification properties.Optical sensor (1) according to one of Claims 19 to 22, characterized in that the operating state of a threshold value switch (12, 12a, 12b, 12c) is determined by evaluations of rising and / or falling edges of received signals and / or temporal hysteresis and / or amplitude hysteresis.An optical sensor according to any one of claims 1 to 23, characterised in that the or each switching unit (14) is controlled by a controller.Optical sensor (1) according to claim 24, characterised in that a plurality of switching units (14) are present, which are controlled individually, in groups or jointly by the controller.Optical sensor (1) according to one of claims 24 or 25, characterised in that the controller controls signal switches (15a to 15d) of the switching unit (14).Optical sensor (1) according to one of Claims 24 to 26, characterized in that control values for the control of the or each attenuation unit (14) are determined in a learning process and are retained unchanged in a subsequent working operation.Optical sensor (1) according to one of Claims 24 to 26, characterized in that control values for the control of the or each changeover unit (14) are constantly tracked in a working operation.Optical sensor (1) according to either of Claims 27 and 28, characterized in that the control values are determined from magnitudes of the received signals after amplification has taken place in an amplifier stage and / or after digitization in a threshold switch (12, 12a, 12b, 12c).Optical sensor (1) according to one of Claims 24 to 29, characterized in that the controller is used to carry out control processes.Optical sensor (1) according to one of Claims 1 to 30, characterized in that it is a safety sensor.Optical sensor (1) according to Claim 30, characterized in that it has a two-channel evaluation unit (9).Optical sensor (1) according to one of Claims 1 to 32, characterized in that it has test means for testing the switching unit (14) and / or elements of the reception paths.Optical sensor (1) according to Claim 33, characterized in that the test means are part of the evaluation unit (9).Optical sensor (1) according to one of Claims 32 and 34, characterized in that a switching over of a reception path takes place via one channel of the evaluation unit (9) and changes in amplification properties for the reception signals which are effected as a result are checked via the further or both channels of the evaluation unit (9).Optical sensor (1) according to one of Claims 33 or 34, characterized in that, for testing, the switching over of reception paths are changed in predefined time intervals and the switching units (14) are tested by ascertaining the signal differences of reception signals obtained in this case.

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